For the Denver connection, you can ask in the Denver Forum.
You need to say what the airlines are and if you have booked your flights on one ticket, not two separate tickets. Your airline’s website should have MCTs (Minimum Connection Times) for the Denver airport.
US Immigration and Customs will be done in Montréal before you board your flight to Denver. Allow 2 hours to go through all the boarding procedures (check in, US customs, US style security).
I can’t speak to whether or not you have the correct entry documents for the USA.